The present invention relates to wireless telecommunication systems, and more particularly to methods and apparatuses that enable multiple radio systems to operate in close proximity using adjacent frequency bands.
When a few decades ago, spectrum regulations were changed to allow commercial radio applications in unlicensed bands, interest was marginal. But this interest has changed radically in the last few years. After the worldwide success of mobile telephony in licensed bands, capacity limitations and huge license fees have spurred the interest of radio applications in the unlicensed band. In the past few years, communications systems such as those operating in accordance with the Wireless Local Area Network (WLAN) IEEE 802.11a and 802.11g standards and the Bluetooth® standards have been increasingly deployed in the 2.4-2.4835 GHz band. Moreover, new communications systems are being worked on, such as the Wireless Personal Area Network (WPAN) activity under IEEE 802.15.
Radio spectrum, even unlicensed, is limited. Despite this, ubiquitous communications using several different standards is foreseen in the near future. Coexistence is not trivial as different standards follow different protocols. Moreover, regulations, initially intended to provide fair sharing, are constantly changing to allow for higher data rates, yet moving away from robustness requirements. The use of an unlicensed band poses the challenge of coexistence. In the design phase of a new communication system that has to operate in the unlicensed band, the developer has to design units that will be expected to share the band with:                Incumbent non-communications: Power unintentionally radiated by equipment, for example microwave ovens, will be a source of disturbance.        Incumbent communications: Intended radiation by other communication systems like for example WLAN, Bluetooth®, or Radio Frequency-Identification (RF-ID) will also be experienced as disturbance when no coordination is applied.        Future systems: Systems that do not exist yet but which will be built in the future can cause severe disturbances. The only known factors are the restrictions imposed upon these systems by the regulations. However, as discussed before, regulations are changing over time, making predictions rather unreliable.        
Coexistence can be handled in a number of different ways, as will now be discussed.
One way of enabling coexistence is by arranging for the different systems to use time division multiplexing (TDM). One aspect of coexistence by means of time division is that it usually requires some kind of collaboration between the systems. For instance, if it is known by one system that another system is receiving, the former might delay its transmission so as not to interfere with the latter. Alternatively, if the latter system knows that reception occurred while the former was transmitting, then it might choose not to use the probably corrupted information and instead to rely on powerful coding and time interleaving and/or possibly retransmission mechanisms as alternative ways of obtaining the information. Because at least one of the systems typically will be affected in a negative way, the overall data rate transmitted will be lower than if a solution permitting simultaneous operation had been feasible.
Another way of enabling coexistence is by means of frequency division multiplexing (FDM), which is an arrangement in which the different systems use different frequencies. Such arrangements allow for the several systems to operate concurrently, so the operation of one does not interrupt operation of another. However, in order to allow for a coexistence solution based on frequency division, a guard band (i.e., a portion of the radio spectrum that is not used by either of the systems) is needed between the two systems to allow for feasible filters to attenuate the signals. Concerning the required attenuation, there are two things that must be considered. One of these is that the filter must ensure that the out-of-band (OOB) emissions of one system are sufficiently low enough to avoid causing an unacceptable degradation of the other system's ability to receive signals. A second consideration is that the filter must ensure that the receiver front-end is not saturated.
Presently, the Industrial, Scientific and Medical (ISM) band at 2.4-2.4835 GHz is used both by Bluetooth® technology and by WLAN technology (i.e., operating in accordance with IEEE standards 802.11b and/or 802.11g). All combinations of these incompatible technologies can be found in mobile phones and similar devices, and the percentage of phones that will have both Bluetooth® and WLAN technology built into them will increase in the future. The bands used for the cellular standards, like the Global System for Mobile Communication (GSM) and Wideband Code Division Multiple Access (WCDMA) are today located several hundred MHz away from the ISM band, and ensuring co-existence between for instance Bluetooth® technology and the cellular standards has been easily achieved by means of filtering. However, with the introduction of technology built in accordance with the Worldwide Interoperability for Microwave Access (WiMAX) and 3GPP Long Term Evolution (LTE) standards, which might be used in the 2.3-2.4 GHz band, filtering might not be sufficient to ensure coexistence because there is no guard band between these systems' radio spectrum and the ISM band. (As used herein, the term “guard band” is used in the conventional sense to mean an unused portion of radio spectrum between two frequency bands.) Both WiMAX and LTE are supposed to use time division duplexing (TDD) in the 2.3-2.4 GHz band, which is denoted “band 40” within 3GPP. In a TDD arrangement, bidirectional communication is achieved by, at times, using one or more frequencies for transmission and, at other times, using the same frequencies for reception.
As these various communication devices become smaller, the number of transceivers in different devices like mobile phones, personal digital assistants (PDAs), laptop computers, and the like is increasing. This means that co-existence between different systems is an issue that can be expected to become even more pronounced in the future.
Therefore, it is desirable to have methods and apparatuses that enable various radio communication systems to coexist with one another in an efficient way that seeks to maximize quality of performance while minimizing any wasting of system resources.